The purpose of the study is to examine the long-term structural and functional effects of cryotherapy as a treatment for severe retinopathy of prematurity (ROP). In January 1986, infants weighing less than 1251 g. at birth were first enrolled in prospective examinations sequence that led to the participation of 291 infants in a randomized trial of cryotherapy for a specified threshold severity of ROP. Follow-up to age 12 months indicated that cryotherapy reduced the incidence of unfavorable structural outcome by 45.8 percent and the incidence of unfavorable visual acuity outcome by 37.8 percent. Based on the preliminary data, follow-up to age 42 months during Phase II of the study indicates that cryotherapy reduced the incidence of unfavorable structural outcome by 39.1 percent. As for vision, cryotherapy reduced the incidence of unfavorable resolution acuity outcome by 21.4 percent, and by 19.7 percent when based on measurement of recognition acuity. The diminished outcome difference between the treated eyes and he untreated eyes, particularly for visual acuity, raises sufficient uncertainty that it is deemed vital to continue following this population until the impact of cryotherapy on ocular visual development in these patients through childhood can be firmly established. The study is currently scaled down, following up all the randomized patients (n=256) and only the natural history study population at the Philadelphia Center who did not develop ROP as infants (n=104). They will be followed through age 10 years, to determine whether the reduction in the benefit of cryotherapy suggested by the data between ages 12 and 42 months will continue into mid-childhood. Evaluation of outcome and the effects of cryotherapy will be based on examination findings in he posterior pole of the eye and on assessment of vision. In addition to acuity, vision will be assessed at age 10 years through measurement of the extent of the visual field by Goldmann perimetry contingent on feasibility determination through a pilot study, currently underway.